全文获取类型
收费全文 | 4639篇 |
免费 | 596篇 |
国内免费 | 1119篇 |
专业分类
化学 | 5687篇 |
晶体学 | 127篇 |
力学 | 11篇 |
综合类 | 32篇 |
数学 | 311篇 |
物理学 | 186篇 |
出版年
2024年 | 11篇 |
2023年 | 60篇 |
2022年 | 124篇 |
2021年 | 211篇 |
2020年 | 273篇 |
2019年 | 266篇 |
2018年 | 177篇 |
2017年 | 207篇 |
2016年 | 278篇 |
2015年 | 272篇 |
2014年 | 338篇 |
2013年 | 485篇 |
2012年 | 329篇 |
2011年 | 281篇 |
2010年 | 243篇 |
2009年 | 283篇 |
2008年 | 305篇 |
2007年 | 324篇 |
2006年 | 283篇 |
2005年 | 249篇 |
2004年 | 227篇 |
2003年 | 195篇 |
2002年 | 152篇 |
2001年 | 96篇 |
2000年 | 95篇 |
1999年 | 71篇 |
1998年 | 54篇 |
1997年 | 64篇 |
1996年 | 55篇 |
1995年 | 71篇 |
1994年 | 51篇 |
1993年 | 30篇 |
1992年 | 50篇 |
1991年 | 37篇 |
1990年 | 27篇 |
1989年 | 27篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有6354条查询结果,搜索用时 578 毫秒
161.
Dominik Huber P. G. Anil Kumar Paul S. Pregosin Igor S. Mikhel Antonio Mezzetti 《Helvetica chimica acta》2006,89(8):1696-1715
Chloride abstraction from the half‐sandwich complexes [RuCl2(η6‐p‐cymene)(P*‐κP)] ( 2a : P* = (Sa,R,R)‐ 1a = (1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐1‐phenylethyl)]phosphoramidite; 2b : P* = (Sa,R,R)‐ 1b = (1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐(1‐(1‐naphthalen‐1‐yl)ethyl]phosphoramidite) with (Et3O)[PF6] or Tl[PF6] gives the cationic, 18‐electron complexes dichloro(η6‐p‐cymene){(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐phenyl]ethyl}[(1R)‐1‐phenylethyl]phosphoramidite‐κP}ruthenium(II) hexafluorophosphate ( 3a ) and [Ru(S)]‐dichloro(η6‐p‐cymene){(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐naphthalen‐1‐yl]ethyl}[(1R)‐1‐(naphthalen‐1‐yl)ethyl]phosphoramidite‐κP)ruthenium(II) hexafluorophosphate ( 3b ), which feature the η2‐coordination of one aryl substituent of the phosphoramidite ligand, as indicated by 1H‐, 13C‐, and 31P‐NMR spectroscopy and confirmed by an X‐ray study of 3b . Additionally, the dissociation of p‐cymene from 2a and 3a gives dichloro{(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐(1‐(η6‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP)ruthenium(II) ( 4a ) and di‐μ‐chlorobis{(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐1‐(η6‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP}diruthenium(II) bis(hexafluorophosphate) ( 5a ), respectively, in which one phenyl group of the N‐substituents is η6‐coordinated to the Ru‐center. Complexes 3a and 3b catalyze the asymmetric cyclopropanation of α‐methylstyrene with ethyl diazoacetate with up to 86 and 87% ee for the cis‐ and the trans‐isomers, respectively. 相似文献
162.
163.
Solvent extraction of a mixture of PbII, MnII, FeIII, CoII, NiII and CdII in aqueous perchlorate medium by a phosphorylated hexahomotrioxacalix[3]arene (calix‐3) in dichloromethane shows a significant selectivity towards lead ions. The ligand can also be incorporated into a membrane to provide a new lead ion‐selective electrode (PbII‐ISE). A plasticized PVC membrane containing 30% PVC, 53.5% ortho‐nitrophenyloctylether (NPOE), 4.5% sodium tetraphenylborate (NaTPB) and 12% ionophore was directly coated on a graphite rod. This sensor gave a good Nernstian response of 29.7 ± 0.7 mV decade?1 over a concentration range of 1 × 10?8 – 1 × 10?4 M of lead ions, independent of pH in the range 3‐7, with a detection limit of 0.4 × 10?8 M. The dynamic response time of the electrode to achieve a steady potential was very fast and found to be less than 7 s. The selectivity relative to Ag+, NH4+, Li+, Na+, K+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Fe3+, La3+, Sm3+, Dy3+, Er3+, Y3+ and Th4+ was examined. The electrode exhibits adequate stability with good reproducibility (with a slope of 29.6 ± 1.5 mV for 8 weeks). The characteristics of the sensor are compared with those of a tetraphosphorylated calix[4]arene (calix‐4) based PbII‐ISE, reported recently. The electrode was successfully used as an indicator electrode for a potentiometric titration of a lead solution using a standard solution of EDTA. The applicability of the sensor for lead ion measurements in various synthetic samples was also investigated. 相似文献
164.
Silver(I)‐Selective PVC Membrane Potentiometric Sensor Based on a Recently Synthesized Calix[4]arene
《Electroanalysis》2006,18(10):1019-1027
A new PVC membrane potentiometric sensor for Ag(I) ion based on a recently synthesized calix[4]arene compound of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐dihydroxy‐calix[4]arene‐thiacrown‐4 is developed. The electrode exhibits a Nernstian response for Ag(I) ions over a wide concentration range (1.0×10?2?1.0×10?6 M) with a slope of 53.8±1.6 mV per decade. It has a relatively fast response time (5–10 s) and can be used for at least 2 months without any considerable divergence in potentials. The proposed electrode shows high selectivity towards Ag+ ions over Pb2+, Cd2+, Co2+, Zn2+, Cu2+, Ni2+, Sr2+, Mg2+, Ca2+, Li+, K+, Na+, NH4+ ions and can be used in a pH range of 2–6. Only interference of Hg2+ is found. It is successfully used as an indicator electrode in potentiometric titration of a mixture of chloride, bromide and iodide ions. 相似文献
165.
一维链状配位聚合物[Cu3(TFSSB)2·(H2O)4·4H2O]n的合成和晶体结构 总被引:4,自引:0,他引:4
The title complex [Cu3(TFSSB)2·(H2O)4·4H2O]n (TFSSB=taurine 3-formylsalicylic schiff base) was synthesized by TFSSB and copper(Ⅱ) acetate monohydrate in ethanol solution and the crystal structure was determined by X-ray diffraction method. The crystal belongs to monoclinic system, space group P21 / n,with cell parameters: a=0.927 9(6) nm, b=1.173 0(2) nm, c=1.471(2) nm, β=106.96(2)°, and V=1.531(2) nm3, Z=2, Dc=1.890 g·cm-3, μ=2.291 mm-1, F(000)=882, R1=0.025 9, wR2=0.065 9. The Cu1 is five-coordinate, the Cu2 is four-coordinate. CCDC: 253298. 相似文献
166.
The coordination compounds of acctylacetonate-5,10,15,20-tctrasubstituted phcnyl-porphyrin with Yttrium, Y(o-Cl)Tppacac, Y(m- Cl)Tppacac, Y(p-Cl)Tppacac, Y(o-CH3O) Tppacac, and Y(p-CH3O)Tppacac (H2Tpp: tetraphcnylporphyrin, Hacac: acetylacctonc), were prepared and characterised on the basis of elemental analysis, infrared spectra, UV-visiblc spectra and thermal analysis. 相似文献
167.
Full details on a very efficient transamination reaction for the synthesis of zwitterionic N,N-dialkyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium derivatives [C6H2(=NHR)2(=O)2] 5-16 are reported. The molecular structures of zwitterions 5 (R=CH3) in 5.H2O, 13 (R=CH2CH2OMe), 15 (R=CH2CH2NMe2), and of the parent, unsubstituted system [C6H2(=NH2)2(=O)2] 4 in 4.H2O have been established by single-crystal X-ray diffraction. This one-pot preparation can be carried out in water, MeOH, or EtOH and allows access to new zwitterions with N-substituents bearing functionalities such as -OMe (13), -OH (9-12), NR1R2 with R1 = or not equal R2 (14-16) or an alkene (8), leading to a rich coordination chemistry and allowing fine-tuning of the supramolecular arrangements in the solid state. As previously described for 15, which reacted with Zn(acac)2 to afford the octahedral Zn(II) complex [Zn[C6H2(NCH2CH2NMe2)O(O)(NHCH2CH2NMe2)]2] (20), ligands 13 and 16 with coordinating "arms" afforded with Zn(acac)2 the 2:1 adducts [Zn[C6H2(NCH2CH2X)O(=O)(NHCH2CH2NX)]2] 19 (X=OMe) and 21 (X=NHEt), with N2O4 and N4O2 donor sets around the octahedral Zn(II) center, respectively. Furthermore, zwitterions 15 and 16 reacted with ZnCl2 to give the stable, crystallographically characterized Zn(II) zwitterionic complexes [ZnCl2[C6H2(NCH2CH2NR1R2)O(=O)(NHCH2CH2NHR1R2)]] 22 (R1=R2=Me) and 23 (R1=Et, R2=H) by means of an unprecedented, tandemlike synthesis in which 1) the two pendant amino groups of the organic benzoquinonemonoimine zwitterionic precursor favor metal coordination and proton transfer and 2) the saturated linker prevents pi-conjugation between the charges. The nature of the structural arrangements in the solid state for both inorganic (20, 22, 23) and organic (5, 9, 13, and 15) molecules is determined by subtle variations in the nature of the N-substituent on the zwitterion precursor. 相似文献
168.
Chun Li 《Tetrahedron》2004,60(37):8037-8041
It has been confirmed that octasulfonatocalix[8]arene (Calx-S8) and tris(2,2′-bipyridine)ruthenium (II) (Ru(bpy)32+) can form a stable host-guest complex in aqueous solution. The binding constant for 1:1 [Calx-S88−·Ru(bpy)32+]6− complex formation was estimated to be (2.4±0.8)×104 dm3 mol−1 by fluorescence titration, which indicates that the [Calx-S88−·Ru(bpy)32+]6− complex is the main species in 1:1 molar ratio aqueous solution of Calx-S8 and Ru(bpy)32+. In situ UV-Vis spectroscopic measurements indicated that Ru(bpy)32+ complexes can be readily deposited onto ITO electrode through electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) using [Calx-S88−·Ru(bpy)32+]6− host-guest complex as a dopant anion owing to the electrostatic interaction between the cationic conductive polymer and the anionic host-guest complex. The loading degree of the composite film with Ru(bpy)32+ can be determined by Lambert-Beer law modified for the two-dimensional concentration. The obtained composite film showed good photoelectric conversion properties in response to visible light irradiation. This is a novel photocurrent generation system in which the photoexcited state energy is efficiently collected by the conductive polymeric layer. 相似文献
169.
Thermal investigations of two novel coordination compounds, potential precursor of copper sulfides, namely [Cu2(S2O3)2(NH3)4]·5H2O and Na2[Cu4(S2O3)5(NH3)8]·2H2O were performed either in solid state (static air atmosphere), as well as in reaction medium. During both decompositions,
Cu2+ reduction occurs. In solid state decomposition, a mixture containing sulfides and sulfates is observed. In the reaction medium,
CuSy compounds with sulfur content y (0.66<y<1) dependent on thiosulfate concentration are obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
170.
Aromí G Ribas J Gamez P Roubeau O Kooijman H Spek AL Teat S MacLean E Stoeckli-Evans H Reedijk J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(24):6476-6488
Coordination complexes of the ligand H3L [1,3-bis(3-oxo-3-phenylpropionyl)-2-hydroxy-5-methylbenzene] with Cu(II) are reported. Clusters showing various nuclearities or modes of supramolecular organization have been prepared by slightly changing the reaction conditions and have been crystallographically characterized. The reaction of H3L with one equivalent of Cu(OAc)2 in DMF yields the dinuclear complex [Cu2(HL)2(dmf)2] (1). Reaction in MeOH of H3L with an increased amount of metal, in the form of Cu(NO3)2, and excess strong base (nBu4NOH) affords the cluster [Cu8(L)2(OMe)8(NO3)2] (2). Complex 2 is a dimer of two linear [Cu4] arrays bridged by methoxide ligands, where the polynucleating ligand is fully deprotonated. The [Cu4]2 clusters are linked to each other by NO3- bridges to form one-dimensional coordination polymers. The link between [Cu8] units and their relative spatial positioning can be modified by changing the anion of the Cu(II) salt, as demonstrated by the synthesis of the cluster polymers [Cu8(L)2(OMe)8Cl2] (3) and [Cu8(L)(OMe)7.86Br2.14] (4), where only NO3- has been replaced by Cl- or Br-, respectively. Similarly, when ClO4- is used, compound [Cu8(L)2(OMe)8(ClO4)2(MeOH)4] (5) can be isolated. It contains independent [Cu8] units. A slight change in the stoichiometry of the reaction leading to 2 affords the related complex catena-[Cu4(L)(OMe)3(NO3)2(H2O)0.36] (6). This polymer contains essentially the same [Cu4] moiety as 2, albeit organized in a completely different arrangement. Each [Cu4] unit in 6 is linked by OMe- ligands to two such equivalent groups to form an infinite chain. Magnetic susceptibility measurements reveal weak antiferromagnetic exchange between Cu(II) centers in 1 (J = -0.73 cm(-1)) and strong antiferromagnetic coupling within [Cu4] chains in 2, 5, and 6 (most negative J values of -113.8 and -177.3 cm(-1) for 2 and 6, respectively). 相似文献